Cellulose is a linear polymeric molecule comprised of D-glucose units bonded by .beta.-1,4-glucosidic linkages. The degree of polymerization (based on D-glucose) can range up to 30,000 or more. Common sources of cellulose include cotton containing approximately 90% cellulose and wood containing generally about 45% cellulose. Cellulose represents the most abundant, renewable organic material on earth. This readily available resource has been considered as potentially valuable as a starting material for the production of food, fuel and chemicals. One important approach has been the isolation and characterization of enzymes capable of degrading cellulose to provide glucose. These enzymes denominated as cellulases have been the subject of several recent review articles (Ghose, T. K., In: "Adv. in Biochem. Eng", Fiechler, Acd., Springer-Verlag. Berlin (1977) and Gong, C. S. et al. In: "Ann. Rev. of Ferment. Proc.", Perlman, D. ed. Academic Process, New York (1979)). It should be noted that cellulase as used herein refers to a group of enzymes which catalyze the hydrolysis of the .beta.-1,4-linkages of the cellulose substrate. Three components of the enzyme system have been recognized and each has been designated by a variety of names by workers in the field. The first component, hypothesized to modify native cellulose of high crystallinity, thus rendering it more susceptible to further degradation, is referred to as .beta.-glucan cellobiohydrolase and also known as C.sub.1, exoglucanase, exocellulase, avicelase, or cellobiohydrolase. The second component, believed to be responsible for the majority of the degradation reaction, is referred to as .beta.-glucan glucanohydrolase and also known as C.sub.x, endoglucanase, endo-.beta.-glucanase or CMCase. The third component which catalyzes the hydrolysis of cellobiose to glucose, is referred to as .beta.-glucosidase and also known as cellobiase.
The biological reduction of N.sub.2 (dinitrogen) to ammonia is known as `diazotrophy, or biological nitrogen fixation. This biological process is unique to procaryotic organisms amongst which it is relatively widespread. The enzyme system responsible for this process is known as the nitrogenase system. It is similar in all the bacteria examined to date and consists of two components; dinitrogenase (the molybdoprotein) and dinitrogenase reductase (the iron protein). (See for example J. R. Postgate, "The fundamentals of nitrogen fixation," 1982, Cambridge University Press, Cambridge).
As the references above indicate, cellulases from a variety of organisms have been studied with respect to their potential uses in industrial processes. Likewise, diazotrophy (nitrogen-fixation) is of considerable industrial and agricultural importance. It is the object of the invention to provide a bacterium that is capable of both cellulose digestion and nitrogen fixation. A bacterium has been isolated from the gland of Deshayes in teredinid molluscs and is novel because it is the first bacterium known to both digest cellulose and fix nitrogen.
The wood-boring shipworms make up a group of bivalve molluscs known as the Teredinidae. These economically important molluscs have received considerable notoriety both historically and presently because of the damage they cause to wooden ships and timber structures in seawater. They are abundant globally and especially prevalent in the tropics, with 14 genera and 67 species currently recognized.
The gland of Deshayes is unique to the Teredinidae. It was discovered more than a century ago by Deshayes (Deshayes, G. P. Explor. Sci. d'Alger. Zool. 1: 35 (1848)) and subsequently named and described by Sigerfoos (Sigerfoos, C. P., Bull. Bur. fish. 27: 191 (1908)). To date, functions ascribed to this gland have been inferred largely from circumstantial evidence. They include the production of cellulolytic enzymes (Morton B., Oceanogr. Mor. Biol. 16: 107 (1978)) and the synthesis of amino acids (Trytek, R. E. et al. Comp. Biochem. Physiol. 67: 149 (1980)). The gland consists of a brown, irregular mass or tissue lining the gill lamellae. Two ducts, one for each gill lie laterially adjacent to the gland in the afferent branchial vein and extend from the posterior to the anterior portion of the gill where they appear to join the esophagus. Popham and Dickson (Popham J. D. et al. Mar. Biol. 19: 338 (1973)) using transmission electron microscopy showed in several species of shipworms that the gland contains numerous rodshaped, Gram-negative bacteria.